Is the problem that there are lots of mediocre artists but not many who can actually execute projects? Or that it is hard to parallelize things like this? Or that once you parallelize too much, the amount of value added by a marginal artist is not enough to pay them?
I think part of it is that standards keep increasing. Compare this demon concept art from Warcraft 2 (1995): http://vignette2.wikia.nocookie.net/wowwiki/images/c/cb/Daem... to this one from WoW: Legion (2016): https://s-media-cache-ak0.pinimg.com/736x/56/f2/7f/56f27f98a...
There are probably a lot of artists that can execute at the 1995 level who aren't employable in 2016.
I would imagine artists need to be involved in technical discussion and would need to learn & bug-test custom software for importing and processing assets. It seems like a different skillset to traditional art & design backgrounds.